Motion compensated transform coding has been widely adopted in various coding standards, where block transform is applied to motion-compensated residues. The motion compensated inter-frame coding system also uses intra-frame mode periodically or adaptively. During the coding process, transform coefficients are quantized in order to reduce bitrate and consequently artifacts are introduced. The artifacts are more visible at boundaries around transform blocks. In order to alleviate the coding artifacts, a technique called deblocking has been developed which applied filtering across block boundaries adaptively. The deblocking technique is also called deblocking filter in the field of video coding.
While the conventional deblocking filter has shown to reduce coding artifacts, the process might have been applied unnecessarily in some circumstances. Furthermore, the deblocking filter may be designed with characteristics to improve performance. Accordingly, it is desirable to design a new deblocking filter to avoid applying deblocking filter unnecessarily and consequently to deliver improved performance.